Yeah I was thinking about just putting it on it's edge but I don't know If I have enough room since it will be snug against the ceiling with my plans currently but there's always time for improvements.

Hmm I know what an I beam is but I've only seen metal ones. With 2x4's would I attach the boards lengthwise with the two 4in side connecting to the middle boards 2'' sides?

That is way overkill.
You can span a 2x4 eight foot and the weight of the light/rail and mover will not effect it at all.
We are only talking about 20-30lbs man.

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alright it's good to have somone shine some light on this. I didn't think it would be a problem since I saw someone else doing it my way with only one 2x4, but they have a slightly different set up so i didn't know.

OK, well I think I'm gonna go start building this thing with the original plan so there will be no hassle in having to wait another day or two for support issues that aren't really going to be that big of a deal, and I can FINALLY start to grow after a year and a half of planning and waiting.

The 2x4 should have a natural bend to it. You can see it by looking down the length of it. Place the wood so that that bend makes a natural arch. It'll give you a bit more strength and prevent sagging.

That's not to say you need to keep a big 'wow' in the board. You can straighten it out. It's just a matter of deciding which side of the board to have facing down for the most support.

If the light and rail are 20-30 lbs and the rail doesn't add any structural support, you'll want to anchor the 2x4 to the ceiling or provide some other extra support.

wake up to the real world, timber is wet when cut down, it gets wetter when transported up and down river as floating logs, once it gets to the mill, it is machine cut to size and very heavy.
it MUST be dried naturally to avoid warpage, this can take longer than the materials are needed.

and a 10 foot long 4" x 2 " thick piece of dried timber placed between two solid columns dried out will easily support the average car engine on a chain.

it will bend, it wont snap, it wont warp, warp is a natural process, bending is not.
if it is allowed to warp through negligence the length of timber will twist like a corkscrew at the same time as it starts to bend with drying out too fast.

if it is fixed between two sheets of timber, or plaster, or drywall, in a building it will not twist and bend in a million years, it will dry out and creak and that is all, although when damp or wet will blunt any decent sharp saw whether electric or hand.

the heat in the building will dry it out totally with age too and its strength increases.
take a damp twig and bend it, now take a dried twig, it is stronger and harder to bend but will snap if bent too far, it is also lighter.

so there you have it.

a piece of 4 x 2 will support huge weights if used alongside other 4 x 2, but...... if it gets too long and used alone it will bend like a banana if the weight exceeds the mass.
but it will take a lot of punishment.

You can also span a 2x4 eight foot with zero weight and have it warp on it's own. I take it you have little experience with carpentry?

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Yes as a matter of fact I have. I built my greenhouse for example. The other thing I have is common sense. Hes not building a house, its a temporary structure just to hold up a light. I agree a 2x4 can warp on its own, if it does, turn it over and mount it again, no big deal. I would recommend he put it on edge though don't mount to the flat side.